I’ve suggested this elsewhere, but instead of simply changing unit values, we just change unit mechanics.
The issue many times with Allied landings in Europe is not that you cannot win an amphibious landing, but are unable to hold it after winning. The amount of transports required by the US to not only land 10 units / round but to continue to do so turn after turn is immense. Its in the range of 20-25 TT in the Atlantic alone not counting the units to fill those TT or the ships to defend them. The US economy may be strong comparatively, but go 100% Atlantic investment and calculate how many IPC you require to effectively project force in Europe and how long it will take to amass the units required and position them to do so.
So my suggestion has been to enable ALLIED surface combat ships to carry solely infantry across the ocean if they take a single hit, and if they can take two hits they have the option of carrying a piece of equipment instead (ART/MEC/ARM). These units can only be moved off combat ships in a NCM move.
1. Reinforcement of an initial wave
2. Reinforcement to reload TT and advance when island hopping in the Pacific
When looking at Germany, it has 2 Majors and 2 Minors in Europe that it can place units; one of those minors are potentially lost if the Allies land on Normandy. Italy has another Major and typically a Minor (S.France) that can reach most Allied landing locations in Europe with MEC/ARM.
The Allies require at least 10 units a round from the US and another 8-10 from the UK to combat an Axis full investment to repel them. If the Allies give the Axis a single round of breathing room where you do not reinforce or introduce more combat units in theater, you have effectively given back the territory you first claimed from to the Axis. There is simply too much Axis production capacity to hold a territory in Europe otherwise.
To combat this, you either need the Allies to arrive earlier to force Germany to divert investments to sack Moscow, or enable the Allies to develop a front they can potentially hold - which requires a constant supply line.
To achieve the latter you can either:
Expand TT capacity
Lower the price of TT
Introduce new transport capacity
Introducing the Allies to Europe earlier is really a mechanic of slowing Germany down in Russia that would force Germany to divert units to fight on two fronts, not speeding up the Allies ability to move across the Atlantic.